Byeong Hwa Kim

Estimation of tension force in double hangers by a system identification approach

This article suggests a new technique for the estimation of tension of a double hanger cable system that is often used in a suspension bridge. The considered hanger system consists of the two independent parallel hanger cables tied by a lateral clamp. Measuring natural frequencies of the system, the hanger tension is determined by a frequency-based system identification technique with the aid of a finite element analysis. The proposed technique is able to simultaneously identify the tension, flexural rigidity and axial rigidity of the target hanger cable system. Laboratory experiments show that estimation errors of the proposed approach are less than 3%. For a relatively long hanger system in the field, the estimated results are similar to those evaluated by the existing methods. However, a significant difference is observed in a short hanger cable system.

Extracting Modal Parameters of a Layered Stone Pagoda Using TDD Technique

This work introduces a modal testing and analysis results of the mock-up for a layered stone pagoda. The pagoda has been horizontally excited by an impact hammer. As to the measured acceleration time responses, the first five lower mode shapes and natural frequency are extracted by the TDD technique. It is observed that the time delay of a shear wave occurs through friction surfaces. Such phenomena cannot be described by using the traditional analytical models such as a continuum cantilever beam model or a discrete shear building model. However, the time delay typically affects only the phases of the pagoda system. The frequencies of the pagoda system are not affected by such time delay. It is found in the first time that the layered stone pagoda system has a set of closely placed modes in near of natural frequency. It is believed that such modes are due to the friction characteristics in friction surfaces. Based on the stick-slip friction model, it seems that the one of the closely placed mode can be a self-excited one.

Estimating Longitudinal Elastic Wave Velocity of Bonded PSC Tendon

This study proposes a most effective way to estimate longitudinal elastic wave velocity of bonded PSC tendon. Various longitudinal vibration tests are conducted for bonded prestressed concrete beams with different applied prestress levels. To estimate elastic wave velocity from measured structural responses, the various estimation techniques are examined such as utilization of acceleration time history, velocity time history, reflected acceleration time history, measured frequency, etc. The comparison results show that the utilization of filtered acceleration is most effective way in practice to estimate elastic wave velocity in an impact-echo test.

Evaluating Axle Loads of Moving Vehicle Using Bridge Deck Plate Responses

A new algorithm to extract influence sequence has been introduced. Using the resulting influence sequences, a way to identify the axle loads of moving vehicles has been introduced. The approaches are based on an optimal linear filter design theory. The algorithms make use of the strain time histories of a bridge deck plate. The performance of the algorithm has been examined experimentally for a folded deck plate on Yongjong Grand suspension bridge. It turns out that the algorithms are feasible and economical while some further works for the accuracy improvement are expected.

Dynamic Characteristics of Layered Stone Pagoda System

For the dynamic behavior of a layered stone pagoda system, the continuous cantilever beam model or discrete shear building model are often considered as a numerical model. However, the validations of such models have not been fully examined yet. A modal testing and analysis of a layered stone pagoda system reveals that there exist a set of closely placed double modes and the time delay of a shear wave occurs through friction surfaces. Moreover, the modal parameters of aforementioned numerical models do not agree with those of real pagoda structure. This work newly proposes a numerical model that can explain such peculiar dynamic characteristics of the layered stone pagoda system. The validation of the proposed model has been examined through the various experiments.

Seismic Behavior of Concrete Cylinders Reinforced by Outside Lateral Hoops

/ A B S T R A C T /This paper investigates experimentally the confinement effect on concrete. For this purpose, outside lateral reinforcement memb ers made of stainless steel and GFRP were employed. Then, uniaxial compressive tests on concrete cylinders incorporating the members were conducted. A total of 30 cylinder specimens, specifically, 6 unconfined specimens, 12 specimens confined by stainless steel and 12 specimens confined by GFRP, were fabricated. The failure patterns of both unconfined and confined specimens were assessed and discussed based on experimental results. The results proved that the maximum stress and corresponding strains of the cylinders confined using the proposed hoops are increased in comparison with those of the unconfined. This supports that the current work can be u sed for retrofitting concrete members and structures and thus may lead to increased stability of such structures.

A Feasibility Study for Estimating Prestressed Stress on a Steel Wire Using Permeability of Magnetic Flux

This work examines the feasibility for estimating existing tensile stress on a stressed wire using the permeability of magnetic flux. A closed magnetic circuit has been constructed to induce magnetic flux inside a steel wire. With different tension stress levels on a wire, the permeability of magnetic flux on the wire has been measured. Two different experimental case studies have been conducted for the examination of sensitivity of permeability of magnetic flux on the stressed wire. One is a varying-length stress test, and the other is a fixed-length stress test. The results show that the permeability of magnetic flux in the varying-length stress test is inversely proportional to the applied stress, while the permeability in the fixed-length stress test is linearly proportional to the applied stress on the stressed wire. It is thus expected that the permeability of magnetic flux on a wire can be a promising indicator for the inspection of its tensile stress.

Effect of Applied Stress of Unbonded PSC Tendon on Stress Wave Velocity

This study experimentally investigates the effects of applied stress level on the stress wave velocity of unbonded PSC tendon. A set of longitudinal impact-echo tests with respect to several applied prestress levels are conducted for both unbonded prestressed strand and steel wire. The comparison results show that the longitudinal stress wave velocity is linearly proportional to the applied stress level in the case both strand and steel wire. However, the sensitivity of the longitudinal stress wave velocity to the applied stress level is very low. Based on the result of nondimensional analysis, it is postulated that the stress wave velocity is also affected by the tensile strength level.

Estimating Tension Force of Elevator Wire Rope Using Frequency

This study introduces the estimation technique of tension force on elevator wire rope using measured frequencies. The proposed approach estimates tension force of elevator wire rope by appling the measured frequencies into the taut string theory or linear regression technique. Such frequencies are measured by accelerometers attached on elevator wire rope. To validate the proposed approach, the various experimental cases for real elevator wire ropes are conducted. The results reveal that both the taut string theory and the linear regression technique show an error bound of . Thus, in practice, the proposed approach could be used for the estimation of tension force on elevator wire rope.

Estimating Effective Prestress Force on Grouted Tendon by Impact Responses

A way of evaluating effective tensile force on a grouted seven-wire strand embedded in the posttensioned beams has been examined experimentally. The proposed approach makes use of the longitudinal stress wave responses collected at the end of strands induced by a mechanical impact at the other end. The six 8m-long post-tensioned concrete beams have been specially designed and constructed. For each beam, the different tension levels are applied. The impact tests are conducted. The results show that longitudinal frequency, elastic wave velocity, and elastic modulus are nonlinearly increased as the tensile force level increases. It is thus expected that the longitudinal vibration characteristics of the existing bonded tendons can be of promising indicators for the inspection of a tensile force loss.